1. Field of the Invention
This invention relates to a toner and an image forming method which are used in recording methods utilizing electrophotography or electrostatic recording. More particularly, this invention relates to a toner and an image forming method which are used in image forming apparatus such as copying machines, printers and facsimile machines in which a toner image is formed on an electrostatic latent image bearing member, thereafter the toner image is transferred to a transfer material via, or not via, an intermediate transfer member, and the toner image on the transfer material is fixed by heat and pressure.
2. Related Background Art
In printers or facsimile machines making use of electrophotography, in order to minituarize image forming apparatus or to simplify maintenance work, it has been spreaded that a developing assembly unit and a photosensitive drum unit are made into a unit or are integrally held together into a process cartridge.
As a developing system used in such a process cartridge, it is usual to use a one-component developing system as being advantageous to minituarization of the apparatus. In the one-component developing system, a one-component developer (hereinafter also referred to as “toner”) is used, where the toner is provided with electric charges (charged electrostatically) by the friction between a toner layer control member (hereinafter also referred to as “control blade”) and the toner or by the friction between a developer carrying member (hereinafter also referred to as “developing roller”) and the toner, and at the same time thinly applied on the developing roller, and this toner is transported to a developing zone where the developing roller and the electrostatic latent image bearing member are opposed to each other, and develops the electrostatic latent image held on the electrostatic latent image bearing member as a toner image.
This one-component developing system, differently from a two-component developing system which requires carrier particles such as iron powder or ferrite powder, requires no carrier particles and hence can minituarize the developing assembly and reduce the weight. Moreover, since the toner concentration in a two-component developer must be kept at a stated value, the two-component developing system requires a device which detects toner concentration and feeds the toner to the developing assembly, causing the developing assembly to be larger and heavier. On the other hand, the one-component developing system does not require such a device. In this regard, the one-component developing system is advantageous to miniaturization and weight reduction of the apparatus. Further, non-magnetic toners are commonly used as a magenta toner, a yellow toner and a cyan toner which are used for full-color image formation.
Printers and copying machines are also demanded to be apparatus adapted to high-speed printing and copying. To satisfy such demand, it is a subject to be studied how to increase the process speed, and it is important to match a fixing assembly with a toner in that process.
In addition, it is preferable to restrain power consumption and improve usability such as quick-start performance.
In such a fixing process, a fixing assembly of a film heating system has been proposed having a small heat capacity.
In the fixing assembly of a film heating system, a heat-resistant film (fixing film) is held between a ceramic heater as a heating element and a pressure roller as a pressure member to form a nip, and a transfer material or recording material on which an unfixed toner image to be imagewise fixed is kept held is guided between the film and the pressure roller at the nip and is sandwiched and transported along with the film, whereby the heat of the ceramic heater is imparted to the transfer material or recording material at the nip via the film and further the unfixed toner image is fixed to the transfer material surface or recording material surface by heat and pressure by the aid of the pressure applied at the nip.
As features of this fixing assembly of a film heating system, an on-demand type assembly can be set up by using low-heat-capacity members as the ceramic heater and the film, and the ceramic heater as a heat source may be electrified only when the image forming apparatus performs image formation, bringing it into the state of heat generation at a stated fixing temperature. Thus, there are advantages that wait time can be shortened ranging from switching on an electric-source of the image forming apparatus until bringing the apparatus into a state that image formation can be started (quick-start performance), and that the power consumption at stand-by time can be vastly reduced (power saving).
However, such a fixing assembly may be insufficient in respect of the amount of heat as a fixing assembly used in full-color image forming apparatus or high-speed machines which are required to have a large amount of heat, and may cause problems of faulty fixing and gloss non-uniformity of fixed images.
As methods for restraining such phenomena, proposed are, as disclosed in Japanese Patent Applications Laid-open No. H9-311499 and No. H6-59502, a method in which the viscoelasticity of toner is specified, a method in which the flow tester viscosity of toner is specified, and a method in which both of these physical properties are specified. It, however, has turned out that at a certain fixing speed these toners have an insufficient effect of restraining faulty images.